Sunday, June 17, 2007

Nikon D200 Guides

As one of Nikon admirer and this camera I love to have one (soon) I will make a little review on how this little monster can do.

The Basics

The D200 is a completely new body design that seems almost a perfect hybrid of the D50/D70 and D2 series. It has the size, pop-up flash, and battery heritage from the D100/D70/D50 progression, but the feature set, button layout, and menus of the D2 series. The D200 body construction is more like that of a D2, including metal framing and gaskets for weather protection, but in your hands it feels much more like the lower-end cameras due to the smaller size and some external construction cues. The one new thing not shared with other current Nikon camera body is the autofocus system, which we'll get to in detail in a bit. Compared to the D100 it replaced, the D200 has gone way upscale. The D200 is better built, better specified, has many more features, and is much more "pro-like" than "consumer." We've got a lot to talk about, so let's get started.
The sensor in the D200 is a CCD made by Sony that appears for the first time in the D200. 10.2 effective megapixels mean 3872 x 2592 pixel images, enough to produce straight-from-camera prints up to about 11x16" without resizing. The base ISO of the CCD is 100, with third-stop increments up through ISO 1600. You can also boost ISO one more stop, up to an effective ISO 3200.

One aspect of the new CCD that is now controversial (more on the controversy in a bit) is that it supports a four-channel analog-to-digital converter (ADC) to get data off the sensor faster, thus allowing the 5 fps frame rate of the D200. By four-channel, I mean that each of the repeated green photosites as well as the red and blue photosites of the Bayer pattern get dedicated off ramps to a separate ADC. Previous Nikon CCDs used single row transfer mechanisms, meaning that a single ADC processed all information.

It's not known if the CCD is unique to Nikon or whether it will appear in other DSLRs (an important question now that Sony has bought Konica/Minolta's DSLR assets and is about to begin selling DSLRs under its own brand name; both Sony and Pentax have "leaked" that they'll have a 10mp DSLR later this year). However, the four-channel trick appears to be a Nikon-designed one, so it may be that the base sensor appears in other DSLR designs, but not with the high-speed transfer ability. As I write this, the D200 is the only camera using this new sensor, though.

Noise in the D200 sensor stems from four design elements: the four-channel transfers, the smaller APS frame size, the smaller overall size of the photosites, and the lack of in-sensor NR electronics. Had we not had the D2x preceding the D200, there probably would have been a lot of pondering about how well noise would be handled by this new sensor. Specifically, the reduced frame size of the Nikon D200 (compared to a full frame camera) leads to a photosite size of about 6 microns. That works out to about 36 square microns available for light collection. Compare that to the D2h's 9.5 micron size, or over 90 square microns available for light collection. Smaller light capture area means fewer light photons are collected; fewer light photons mean that inherent noise properties of the underlying silicon are higher in relationship to the photon count, which means more noise. On the plus side, CCD sensors tend to have less noise than CMOS sensors, all other factors equal.

Nikon chose to address noise in a number of ways. For example, once again data appears to be kept in 16-bit space right up until the final compression to an 8-bit JPEG (or uncompressed TIFF). Second, data is manipulated in the analog space (electrons) prior to amplification and digital conversion. This is most prevalent where individual channels are amplified prior to the ADC to adjust white balance, but I wonder if it applies to higher ISO values, as well. Finally, the internal digitization engine has a noise reduction component in it (well, actually two different components, one for long exposure noise and another for high ISO noise). When we get to the results section of the review, we'll talk about whether or not Nikon was successful, but note that multiple techniques are once again being employed here rather than a single one.

Other sensor-related items have changed, as well. Once again the anti-aliasing filter seems to have been tweaked. It doesn't seem quite as relaxed as the D70 and D2h, but it isn't as aggressive as the D1 series or D100. The D2x and D200 seem to both be smack dab in the Goldilocks spot of antialiasing: not too much, and not too little. However, note that by not being lax in antialiasing, unsharpened D200 images will look decidedly soft. Meanwhile, the infrared and ultraviolet filtration has been increased yet again--the D200 is a terrible IR or UV camera. Each successive Nikon DSLR seems to have more and more IR and UV filtering. If you want to shoot that type of image, you're either going to have to hold onto those old D1's and D100's, or have a newer DSLR modified to remove that filtration.

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